A space-division switching network is a communication system in which connections from a set of input ports to a set of output ports are established by physically linking paths together by means of switching elements. The term in space-division is used because communication paths are implemented by linking together a dedicated connection in space as opposed to sharing a connection in time.
In most space-division switching networks, the input ports and output ports are linked together in what can generically be referred to as a one-to-one transmit/receive arrangement. These one-to-one transmit/receive arrangements are often referred to as permutation connections. Each input port is directly and permanently attached, by means of an appropriate interfacing mechanism, to a transmit port of a transmit station. The transmit station serves as a source of, for example, voice/data information which is fed into the switching network through the input port to which it is interfaced. Each output port is directly and permanently attached, by means of an appropriate interfacing mechanism, to a receive port of a receive station. The receive station serves as a sink or destination of the voice/data information being transmitted through the switching network over the connecting path that has been implemented. In a permutation connection, the communication requirement between the transmit stations and the receive stations is such that, at any time, each input port must be connected to at most one output port. Networks providing such one-to-one connectivity are usually referred to as permutation switching networks.
There exists a class of communication requirements between the transmit stations and the receive stations where the connectivity required of the switching network is much more demanding than one-to-one port pairing in that an input port interfaced to a transmit station must be connected at times to more than one output port (receive station) in a one-to-many fashion. This one to many communication mode is referred to as broadcasting. Generally, in a broadcast connection from a transmit station to receive stations, it is only of interest to connect an output port (receive station) at any given time to at most one input port (transmit station). A broadcast switching network must be capable of simultaneously providing multiple broadcast connections from the input ports to the output ports with the restriction that no output port can ever be connected at a given time to more than one input port.
There have been a variety of techniques developed with respect to switching networks. U.S. Pat. No. 4,402,008 to Teraslinna discloses a wide band switching architecture. The wide band switching architecture allows wide band signals to be communicated through a wide band switching network with minimal crosstalk between the wide band signals. The wide band switching network is comprised of stages, each of which has a plurality of switching input and output arrays. Each input array has one input terminal and each output array has one output terminal. Each array is one integrated circuit, and crosstalk is reduced by allowing only one wide band signal to be present in each integrated circuit at any one time and by grounding all unused outputs and inputs in the arrays.
U.S. Pat. No. 4,696,000 to Payne discloses a nonblocking self-routing nodes. The broadcast nodes are responsive to the transmissions of address information from an input port to create a plurality of paths through the switching network to communicate on this plurality of paths the address information to the routing states. Each of the routing switch nodes is responsive to receipt of address information to select one of the paths to an address designated output port.
U.S. Pat. No. 4,651,318 to Luderer discloses a multistage packet switching network comprising a plurality of pack switch nodes for communicating broadcast and non-broadcast packets. Each node is responsive to receipt of one of the packets. If a broadcast packet has been received, the switch node transmits this packet to the next sequential stage on all output links interconnecting the switch nodes to the next sequential stage. If the packet is of a non-broadcast type, the switch node decodes the state identification field therein to determine which of the sets of the routing information is to be used for routing that non-broadcast packet to the next sequential stage.
U.S. Pat. No. 4,566,008 to Richards discloses a two-stage, rearrangeable multiconnection switching network for connecting N1 input channels to N2 output channels. The network comprises a number of first stage switches and a second stage switch. The second stage switch has N2 outlets, each connected to one of the N2 output channels. A connection arrangement connects each of the first stage switch ringlets to an associated predetermined input channel such that for any group N2 of input channels, there is a group of N2 of the first stage switches, each having one inlet connection to a different on that group N2 of the input channels. This patent to Richards also discloses that the network is extendable by adding second stage switches and connecting each additional second stage switch to each first stage switch. In larger networks, the first and second stage switches are themselves replaceable by two stage networks in accordance with the invention.
The problem that exists in realizing broadcast connections with a space-division switching network is that the network must have a fan-out capability. When fan-out is used to implement a broadcast connection from a single input port to multiple output ports, the resulting connecting path corresponds to a tree of connecting paths through the network where the input port is the root of the tree and the output ports are leaves of the tree. To establish a tree of connecting paths through a space-division switching network using fan-out is significantly more complex than establishing a set of one-to-one connecting paths. See G. M. Masson, "Upper bounds on fan-out in connection with networks,: IEEE Transactions on Circuit Theory", Vol. CT-20, pp. 222-230; 1973. Modifying the state of a space-division switching network employing fan-out to provide a new connection by rearranging trees of connecting paths is prohibitive.
Accordingly, to satisfy a broadcast connection, a space-division network must have connecting capabilities far in excess of that required for the one-to-one or permutation type of connection. To see this, note that a permutation network with N inputs must be able to realize N! assignments of inputs to outputs while a broadcast network with N inputs must be able to realize N.sup.N assignments. Because the switching modules comprising a broadcast network must have fan-out capabilities relative to their inputs and outputs, much of the well-established theory for the design and analysis of permutation networks is not applicable to the broadcast problem. It is the purpose of this invention to illustrate a broadcast switching structure that employs permutation switching modules linked with collections of broadcast modules in such a way that the broadcast modules from centralized hubs which solely provide the one-to-many or fan-out broadcast function.